The length of the moment arm of the force plays a huge role. Anyone can lift their entire bodyweight many times in a row with just their small calf muscles (gastrocnemius and soleus). We do it all the time.
Did you ever wonder why monkeys, with similar upper body design as humans, can swing from tree limb to tree limb and climb so easily? Their lats are not more developed than humans. Even newborn monkeys can out climb any human.
I've never seen a monkey at the gym doing pull-ups.
The muscles required to do pull-ups are bigger than those required for push-ups yet most people struggle with pull-ups. Why?
Yes, it is harder to lift your own body weight from the pullup position. You can cheat in any weightlifting exercise in the gym. But it might be hardest to do it with regular pullups. It is easy to cheat in pushups, a friend of mine said he could do over 100 consecutively, but his arms were as skinny as anyone I have ever known. Obviously his form was not perfect! Most people walk around saying they bench pressed 290, yet they cheated. Some people will even go to the gym and use as many as three body builders to spot them in the bench. Those people also voted for you know who.
Triceps for pushups are bigger than biceps. You do use your latimus Doris, rhomboids, and traps for pull-ups and those are big muscles but the bicep itself is not. Your entire chest wall muscles including your deltoids contribute to pushups.
Yes, it is harder to lift your own body weight from the pullup position. You can cheat in any weightlifting exercise in the gym. But it might be hardest to do it with regular pullups. It is easy to cheat in pushups, a friend of mine said he could do over 100 consecutively, but his arms were as skinny as anyone I have ever known. Obviously his form was not perfect! Most people walk around saying they bench pressed 290, yet they cheated. Some people will even go to the gym and use as many as three body builders to spot them in the bench. Those people also voted for you know who.
Basically your question is: why is lifting all of your weight harder than lifting 2/3 of your weight?
For me, it’s less than 2/3. I can do 30+ pushups but am unlikely to bench 2/3 of my weight for that many reps. It’s more like 55-60% of my body weight.
Benching is going to be harder than push-ups on a lbs-for-lbs basis. You need to have a larger margin of excess strength because you're expending additional energy on keeping the bar balanced. Much easier to keep yourself balanced while doing a push-up.
Basically your question is: why is lifting all of your weight harder than lifting 2/3 of your weight?
For me, it’s less than 2/3. I can do 30+ pushups but am unlikely to bench 2/3 of my weight for that many reps. It’s more like 55-60% of my body weight.
I weighed myself in a lowered pushup position a while back, and it was about 75%.